clang++ 3.1，但在Lion Xcode 4.3.3上没有“cxx_lambdas”

这与 Clang 3.1 和 C++11 支持状态有关，但我在那里找不到答案，我在这里更具体：在我的确切设置上对 clang 3.1 cxx_lambdas支持。

我在OSX Lion 10.7.4上安装了Xcode 4.3.3和最新的命令行工具包（2012年6月11日）。我现在有 clang++ 版本 3.1：

llins@jupara:~/projects/tests/C++11$ clang++ -v
Apple clang version 3.1 (tags/Apple/clang-318.0.61) (based on LLVM 3.1svn)
Target: x86_64-apple-darwin11.4.0
Thread model: posix

基于 http://clang.llvm.org/cxx_status.html，我希望cxx_lambdas可用的功能，但这不是我得到的：

llins@jupara:~/projects/tests/C++11$ make
clang++ -std=c++11 -stdlib=libc++ test_clang_features.cpp -o test_clang_features
llins@jupara:~/projects/tests/C++11$ ./test_clang_features 
FAILED feature tests: 
__has_feature(cxx_constexpr) .................................. FAILED
__has_feature(cxx_generalized_initializers) ................... FAILED
__has_feature(cxx_inheriting_constructors) .................... FAILED
__has_feature(cxx_lambdas) .................................... FAILED
__has_feature(cxx_local_type_template_args) ................... FAILED
__has_feature(cxx_unrestricted_unions) ........................ FAILED
__has_feature(cxx_user_literals) .............................. FAILED

这是我为获取此报告而运行的代码：

#include <iostream>
using namespace std;
void main()
{
    cout << "FAILED feature tests: " << endl;
//  testing all features cxx_???? described in (only 3 shown here):
//      http://llvm.org/releases/3.1/tools/clang/docs/LanguageExtensions.html#cxx11
#if !__has_feature(cxx_generalized_initializers)
    cout << "__has_feature(cxx_generalized_initializers) ................... FAILED" << endl;
#endif
#if !__has_feature(cxx_implicit_moves)
    cout << "__has_feature(cxx_implicit_moves) ............................. FAILED" << endl;
#endif
//... analogous tests ...
#if !__has_feature(cxx_lambdas)
    cout << "__has_feature(cxx_lambdas) .................................... FAILED" << endl;
#endif
}

请注意，cxx_lambdas失败了。以下是测试功能的完整列表：

cxx_access_control_sfinae cxx_alias_templates cxx_alignas
cxx_attributes cxx_auto_type cxx_constexpr cxx_decltype
cxx_default_function_template_args cxx_defaulted_functions
cxx_delegating_constructors cxx_deleted_functions cxx_exceptions
cxx_explicit_conversions cxx_generalized_initializers
cxx_implicit_moves cxx_inheriting_constructors cxx_inline_namespaces
cxx_lambdas cxx_local_type_template_args cxx_noexcept
cxx_nonstatic_member_init cxx_nullptr cxx_override_control
cxx_range_for cxx_raw_string_literals
cxx_reference_qualified_functions cxx_rtti cxx_rvalue_references
cxx_static_assert cxx_strong_enums cxx_trailing_return
cxx_unicode_literals cxx_unrestricted_unions cxx_user_literals
cxx_variadic_templates

为什么cxx_lambdas在 clang++ 3.1 的此设置中不可用？